CSEDI: Collaborative Research: Experimental and SIMS Investigation of H2O Storage Capacity of the Mantle

该项目是美国明尼苏达大学的实验岩石学家和亚利桑那州立大学的分析地球化学家之间的合作，旨在解决CSEDI倡议的两个主要目标：(1)了解地球深水循环和(2)了解H2O对地幔熔融、相变和物理性质的影响。明尼苏达大学将利用高温高压装置进行实验，以确定橄榄岩在上地幔、过渡带和下地幔条件下的H2O储存量。储存量是指在一定的温度和压力下，固体橄榄岩中所能保留的最大H2O。储存能力限制了富含H2O的地幔储集层的可能区域和可能的水合熔融地点。由于H2O对地幔蠕变强度、弹性和导电性等性质有很大的影响，它们也对地幔动力学提供了关键的约束。亚利桑那州立大学将使用新开发的低空白二次离子质谱仪技术分析实验产品中微量的H2O。将解决四个相关的实验问题：(1)为了调查最近表明上地幔具有比先前估计的更大的存储容量的迹象，将在3-13千兆帕斯卡的实验中确定橄榄岩H2O的存储容量。(2)为了确定H2O对洋脊和洋岛下深部熔融的影响以及对上地幔脱水的影响，将在3-8 GPa时确定矿物/熔体H2O的分配。(3)为了更好地了解H2O在410公里不连续面上的传输，包括H2O对熔融和相变的影响，将在13-15 Gpa的温度范围内确定H2O的矿物间分配和存储容量。(4)为了帮助解决有关下地幔储存能力的争议，将在22-25 Gpa的压力下进行实验，该压力与670公里不连续区域的压力有关。

This project is a collaboration between experimental petrologists at U. Minnesota and analytical geochemists at Arizona State to address two of the chief goals of the CSEDI initiative: (1) to understand the Earth's deep water cycle and (2) to understand the influence of H2O on melting, phase transitions, and physical properties of the mantle. Experiments to determine the H2O storage capacity of peridotite under upper mantle, transition zone, and lower mantle conditions will be performed using high temperature high pressure devices at the University of Minnesota. The storage capacity is the maximum H2O that can be retained in solid peridotite at a given temperature and pressure. Storage capacities constrain possible regions of H2O-rich mantle reservoirs and possible loci of hydrous melting. Owing to the large effect of H2O on mantle properties such as creep strength, elasticity, and conductivity, they also provide critical constraints on mantle dynamics. Experimental products will be analyzed at Arizona State for trace quantities of H2O using newly-developed low-blank secondary ion mass spectrometry techniques. Four related experimental problems will be addressed: (1) To investigate recent indications that the upper mantle has a larger storage capacity than previously appreciated, experiments at 3-13 Gigapascals will determine peridotite H2O storage capacities. (2) To determine the influence of H2O on deep melting beneath oceanic ridges and oceanic islands and the consequences for dehydration of the upper mantle, mineral/melt H2O partitioning will be determined at 3-8 GPa. (3) To better understand transport of H2O across the 410 km discontinuity, including the effect of H2O on melting and phase transitions, inter-mineral partitioning of H2O and the storage capacity will be determined at 13-15 GPa over a range of temperatures. (4) To help resolve controversy about the storage capacity of the lower mantle, experiments will be performed at 22-25 GPa, pressures relevant to in the region of the 670 km discontinuity.